GB calibration method for dense paste pipe flow measurement

National standard calibration method for dense paste pipe flow measuring device

The thick paste pipe flow measuring device is a flow meter specially developed for experimental research and engineering needs in the field of thick paste. The flow meter must be periodically calibrated before it can be put into use. In order to find a calibration method suitable for the use of a thick paste pipeline flow measuring device, the methods specified in several standards ( weighing method, volume method, standard table method and standard volume tube method ) were analyzed, and the comparison was made *** In the end, only the weighing method and the standard volume tube method can adapt to different thick pastes with different solid content, different conductivity and different fluidity. Therefore, the two methods are recommended as a method for calibrating the thick paste pipeline flow measuring device.

0 Preface

The thick paste has the characteristics of high solid content, high viscosity, fine particles, low electrical conductivity, and slow pipeline flow rate. It is difficult to measure with various known flow meters. Due to the needs of engineering practice and experimental research, a large-scale paste pipeline flow measuring device was independently developed . The device is essentially a velocity flow meter that obtains a flow rate by measuring the flow rate. In order to improve the output accuracy, each flowmeter must be calibrated before it is shipped from the factory, so the thick paste pipe flow measuring device must also be calibrated before it can be put into use.

The current standard GB ( International Standard ISO) calibrating methods for liquid flowmeters include weighing methods ( including static weighing and dynamic weighing ) , volumetric methods ( including static volumetric methods and dynamic volumetric methods ) , standard methods and standards. Volume tube method. Generally, when the manufacturer of the flowmeter calibrates the flowmeter, the standard method or the standard table is combined with the weighing method. To this end, several standard calibration methods were analyzed and a calibration method that could be applied to a thick paste pipe flow measurement device was discussed.

 

Method 1. Weigh

 

Standard GB / T 17612 - 1998 "Measurement Weighing Method for Liquid Flow in Closed Pipes " stipulates that the method of measuring the fluid flow in a closed pipe to determine the fluid flow in a closed pipe at a known time interval is a weighing method . The principle is divided into static and dynamic. As long as the vapor pressure of the liquid does not affect the amount of liquid spillage due to evaporation in the weighing vessel affects the required measurement accuracy ( also known as accuracy ) and ensures that the liquid fills the line and there are no cavitation in the measurement section, Use this method. Because of the high degree of this method, it is necessary to know the liquid density in order to calibrate other mass flow measurements or volume flow measurements as a baseline method.

 

1 . 1 static weighing method

 

1) Basic principles. As shown in Figure 1 , the working process is : determining the initial mass m0 ( peeling ) of the remaining liquid in the container and container . Operate the commutator to allow liquid to flow into the weigh container ( until the amount considered is sufficient to achieve the desired degree ) and start the timer to measure the infusion time t ( discharge, timing ) . Determine the final mass m1 ( weighing ) of the container and the liquid collected in the container .

 

Accordingly, the average mass flow rate qm is the injection period is:

2) Error analysis. Only two main sources of error, system error and random error, are considered.

 

Types of system error sources and methods of elimination :

 

(1) The error caused by the scale ( the position of the knife edge on the scale, the estimation of the atmospheric buoyancy ) , and the replacement weighing technique ( ie, the electronic scale ) can eliminate the former.

 

(2) The error caused by the timing device can be ignored if the timing error is less than 1 ms using modern equipment .

 

(3) The error caused by the commutation system can be eliminated by canceling the commutation system.

 

(4) Error caused by density measurement ( error caused by temperature or density measuring device ) .

 

Random error source types and elimination methods :

 

(1) The error caused by the instrument, the estimation method is given in the standard GB/T 17612-1998 .

 

(2) The error caused by the commutator can be eliminated by canceling the commutation system.

 

1 . 2 dynamic weighing method

 

1) Basic principles. As shown in Figure 2 , the working process is to start the timer when the liquid collected in the container reaches a predetermined initial mass. The timer is stopped when the collected liquid reaches a predetermined final quality. The calculation formula is also the formula (1) and formula (2) .

2) Error analysis. Since the dynamic weighing method does not use a commutator, the error mentioned in the static weighing method is not generated. However, the dynamic weighing method produces errors in the static weighing method, and the elimination method has been mentioned before. The dynamic weighing method is also affected by the following four dynamic phenomena, which may introduce new errors :

 

(1) Injecting a change in liquid impact force between the beginning of the *** and the final focus of the ***.

 

(2) The column of the injection liquid formed due to the elevated liquid level in the container is the amount of additional liquid collected by the container.

 

(3) The force caused by the fluctuation of the liquid in the container.

 

(4) The inertia of the liquid in the scale and the weighing container, with the result that the time required to accelerate the balance scale to the start point of the timer changes.

 

In general, the forces generated by (1) and (2) are equal and opposite in direction and can be offset. In the case of a thick paste in the container, if no significant fluctuations occur, the error caused by item (3) is small. In the standard, based on the balance bar scale size parameter, the estimation formula of the timing approximation error t introduced in (4) is given, and the large value of t is 0 . 5% . In addition, the use of other weighing techniques instead of the balance bar scale can eliminate the error introduced in item (4) , that is, the effects of the four dynamic phenomena on the timing are conditionally eliminated or ignored.

1 . 3 applicability analysis

The weighing method used in the previous research on the characteristics of the thick paste is compared with the above two methods. The principle is in accordance with the static weighing method, but the manual timing is used in the experiment, which does not meet the requirements of the automatic trigger timer in the standard, and the timing must be improved. The method improves measurement accuracy and achieves accuracy that can be used for calibration work.

 

2. volumetric method

 

The volumetric method is divided into a static volumetric method and a dynamic volumetric method. The measuring device is the same as that of Figs. 1 and 2 , except that the weighing instrument is replaced by a measuring cylinder. According to the standard GB / T 3214 - 2007 "measurement method of pump flow" calculation formula is as follows :

Where Vr is the volume of liquid injected into the amount of flux in time t .

Due to the high solid content of the thick paste, it does not have fluidity under normal temperature and pressure, and it is impossible to form a flat liquid surface naturally. It is not suitable for measuring the volume of the measuring cylinder. However, when the solid content of the thick paste is low, it has a certain fluidity, and the volume of the collected thick paste can be measured using a container having a volume measuring function (a measuring cylinder, etc. ) , and the volume flow rate can be calculated by the formula ( 3) .

 

The disadvantage of this method is that it is only suitable for thick pastes with low solid content and certain fluidity, and the advantage is that the mass-to-volume conversion process is omitted, and the error caused by density measurement is eliminated.

3. Standard table method

 

The principle of the standard table method is mainly based on the fluid mechanics flow continuity equation. If a standard meter is connected in series with the calibrated flowmeter ( referred to as the instrument to be calibrated ) , the calibration fluid continuously passes through the standard meter and the metered instrument at the same time interval, and the mass flow Qm flowing through the two tables at any time is equal. By ignoring the difference in fluid density between the two meters, it is considered that the volume flow Qv flowing through the two tables at any time is equal. At the same time, the readings of the standard meter and the meter being read are read, and the output flow of the two is compared to determine the metering performance P of the meter being calibrated .

 

Let K be the ratio of the standard instrument data to the instrument data being measured, that is, the meter factor :

Wherein, Qvs standard volume flow meter for the measurement; QVT correction volume flow meter is being measured.

By analyzing the data of the previous thick paste pipeline transportation experiment, it can be concluded that the precision grade of the thick paste pipeline flow measuring device is 1 . 0 , so the calibration of the thick paste pipeline flow measuring device must use an accuracy level higher than 1 . 0 meter, at least 0 . 5, more than two levels (i.e., greater than 0.1) is a good ***. Due to the high solid content, low electrical conductivity and slow flow rate of the thick paste, only the slime with a solid content of less than 63% can be used, and the flow rate is measured by an electromagnetic flowmeter with an accuracy level of 0 . 5 .

Therefore, this method is also conditionally applicable and not applicable.

 

4. Standard volume tube method

 

The standard volumetric tube method is a spherical or cylindrical object that is driven by a liquid and moves along a standard volume segment, and when it passes through a standard volume segment, it can displace a known volume of liquid between the two detection switches. The displacer has an elastic sealing surface in close contact with the tube wall to prevent liquid leakage, and is divided into a ball type and a piston type. This method was applied early to the oil industry and the standard was upgraded from the petroleum industry standard.

 

Standard 1988 GB / T 9109 . 3—1988 “ Technical Regulations for the Installation of Crude Oil Dynamic Metering Fixed Standard Volume Tubes” introduces the ball type standard volume tube. Only after the ***, a piston type standard volume tube imported from abroad is mentioned. Most of the calibration of this method uses the former, while the latter only imports equipment. In 1998, the standard GB / T 17286. 4-1998 "Liquid Hydrocarbon Dynamic Measurement Volumetric Flowmeter Verification System" has standardized the piston standard volume tube. Many related papers have emerged in the same period. Later, some related specialties were born, which can be seen in the domestic piston type. Become the mainstream of this method.

4 . 1 ball

 

Figure 3 is a schematic diagram of the spherical standard volumetric tube method described in GB/T 13282-1991 "Volume Tube Flow Measurement Calibration Device". The ball displacer is used to discharge the liquid in the standard volume tube between the two detection switches, and the interval time between the signals transmitted by the two detection switches is measured, and the volume flow rate qv is :

4 . 2- piston

 

Figure 4 is a utility model special 201120316770 . A piston type standard volume tube is disclosed in the principle that the piston is used as a displacer to discharge the liquid in the standard volume tube. If the start-stop time interval tp of the liquid discharge is known , and the volume of the standard volume tube is Vp , the volume flow rate qv is :

4 . 3 applicability analysis

Since the driving device for the thick paste pipe is a piston pump, it is also feasible to use the piston standard volume tube method for the thick paste. The accuracy of the volume data of this method is guaranteed by the standard cavity, which avoids the uncertainty of measurement. Only the timing error is generated during calibration, and the precision is high. In addition, the piston type operation is highly automated and is a preferred instrument for calibration.

 

5. Conclusion

 

1) Generally, the physical properties of the thick paste produced in a factory for a period of time should be relatively stable. Therefore, the thick paste pipe flow measuring device should be calibrated to use the thick paste produced by the use of the ground to ensure the accuracy of the measurement output. . This requires the selected calibration method to adapt to different physical characteristics, including different solid content, different conductivity and different fluidity. Therefore, the method that can be applied under certain physical characteristics cannot meet the calibration work of the thick paste pipeline flow measuring device. Through research and analysis, among the four calibration methods, only the weighing method and the standard volume tube method can meet the above requirements.

 

2) According to the standard, the spirit of using advanced scales is adopted. The use of electronic scales instead of the scales in the weighing method standard example can eliminate some errors and improve measurement accuracy, and the improved weighing method can be directly used not only in the field of thick paste research. Measurement of experimental data, and can be used as a reliable calibration method for flow measurement devices in its engineering field.

 

3) At present, there is no standard volume tube specially calibrated with a thick paste. On the one hand, it can be examined whether equipment used in other fields can be directly used in the field, and on the other hand, a standard volume tube suitable for the field can be designed, but the calibration device Must be verified and approved.

 

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